niche vs open fireplace

niche and open fireplace both are nouns.

Word	Noun	Adjective	Verb	Adverb
niche	Yes	No	No	No
open fireplace	Yes	No	No	No

As nouns, open fireplace is a hyponym of niche; that is, open fireplace is a word with a more specific, narrower meaning than niche:

niche: an enclosure that is set back or indented
open fireplace: an open recess in a wall at the base of a chimney where a fire can be built

Other hyponyms of niche include alcove, bay, apse, apsis, cinerarium, columbarium, fireplace, hearth, mihrab.

niche (noun)	open fireplace (noun)
an enclosure that is set back or indented	an open recess in a wall at the base of a chimney where a fire can be built
a small concavity
a position particularly well suited to the person who or organization which occupies it
(ecology) the status of an organism within its environment and community (affecting its survival as a species)